You just say that your parents did such a good job of raising you, and that they trust you so much that they know that even if they do put you 'infront of men' you're not gonna rip of your clothes and become a whore...or something along the lines of that
Co-ed is where the best education lies sometime, universities away from home may be better for you in relation to the course youre taking.
Just because theyre not comfortable with sending their kids away from home, because they dont trust them, doesnt mean everyones parents have the same worries. Each to their own, tell them to get over it.